Colombo, April. 11 (AP): Clashes between Sri Lankan soldiers backed by artillery and Tamil Tiger rebels in the north have killed up to 30 people, the two sides said Wednesday amid a spate of air raids, bus bombings and sea battles that have left scores dead in recent weeks.

Wednesday's statements from the government and rebels offered the first details of the clashes that broke out a day earlier near the frontier separating government- and guerrilla-held areas in northern Sri Lanka _ violence that each side accused the other of instigating.

Much of the fighting since a 2002 cease-fire unraveled over the summer has taken place in eastern Sri Lanka. But there have been occasional clashes in the north, and tension has been mounting around the Omanthai checkpoint, the last post held by the government before the start of Tiger territory.

A military spokesman, Lt. Col. Upali Rajapakse, said unprovoked rebel mortar fire on Tuesday killed a soldier at the checkpoint, forcing the army to respond with its own artillery and mortar fire that left at least 20 insurgents dead. The army also closed the checkpoint.

``The figure may be more, but this is what we have from our intelligence sources,'' Rajapakse said.

He accused the Tigers of deliberately starting the violence ahead of the New Year's celebrations for Sri Lanka's Sinhalese majority and its Tamil minority, in whose name the Tamil Tigers have been fighting since 1983.

The Tigers countered that their fighters had ambushed army soldiers making a push through the nearby jungle into rebel territory, killing eight to 10 of the intruders and seizing weapons and ammunition, including rocket-propelled grenade launchers.

``We have the bodies,'' rebel spokesman Rasiah Ilanthirayan said in a statement posted on a pro-rebel Web site, TamilNet. He added that three insurgents were also killed.

The area is largely off-limits because of the fighting, and it was not possible to independently verify either side's claims.

The Tamil rebels are fighting for a separate homeland for Sri Lanka's 3.1 million Tamils, a largely Hindu ethnic group concentrated in eastern and northern Sri Lanka. The Tamils have faced decades of discrimination from the predominantly Buddhist Sinhalese, who make up a majority of the Indian Ocean nation's 19 million people.

At least 65,000 people were killed before the 2002 cease-fire _ which officially remains in force but has completely unraveled over the last 18 months as tit-for-tat attacks have grown into all-out war. Another 4,000 people, many of them civilians, are estimated to have been killed since late 2005.

The violence has increased dramatically in recent weeks as the government has pushed to overrun Tiger strongholds in the east, where the insurgents are weakest.

Over the last week, the government has bombed the rebels' naval headquarters in the north and clashed with the insurgents in the east and at sea, reportedly killing more than two dozen rebels.

The Tigers have struck back with bombings and several sea attacks. Two bus bombings the military blames on the insurgents killed at least 23 people, and the Tigers in March carried out their first-ever air raid, striking an air force base.